A major goal of well logging is to gain insight into the reservoir and thereby maximize the amount of hydrocarbons recovered from an earth formation and in order to better develop techniques and methods to accomplish this, it is helpful to know as much as possible about the physical characteristics of the earth formation surrounding a well. For example, by continuously monitoring the oil saturation in an earth formation, which is typically expressed as a percentage by volume of oil in the pore space, secondary and tertiary techniques may be developed to use this oil saturation to enhance the recovery of the hydrocarbons.
It is well known in the oil and gas industry that physical characteristics of the formation surrounding a well, such as the chemical content of the formation and the fluid in the formation, may be determined from radiation emanating from the formation, wherein the radiation may be either naturally originating in the formation or the radiation may be induced by irradiating the formation during the well logging operation. As such, scintillation detectors are typically employed to analyze the energy content characteristics of this radiation to enable the determination of pulse-height spectrum characteristics of the gamma-rays being emitted by the formation.
As is also well known, scintillation detectors are used to detect and measure the number and energy of gamma rays present in an earth formation. Typically, a scintillation detector includes a crystal and a photomultiplier, such that when a gamma ray becomes incident upon the crystal, the incident gamma ray imparts energy to electrons in the crystal through Compton scattering, photoelectric absorption, and pair production. This introduction of energy to the electrons in the crystal causes the detector crystal lattice to become excited and when the crystal de-excites, visible or near-visible light is emitted. This scintillation is then detected by the photomultiplier and transformed into an electrical pulse having a frequency and amplitude responsive to the number of gamma rays and their respective energy levels, wherein the characteristics of the electrical pulse is typically recorded in a log for analysis.
One particular type of scintillation detector utilizes Lutetium Aluminum Perovskite, or LuAP, as its scintillation material. LuAP has been known for a number of years and is recognized as a promising host for radiation detection applications due to its exceptional combination of properties, such as high stopping power, very short decay times and reasonably good energy resolution. Unfortunately, however, most current methods for producing LuAP crystals for use in scintillation detectors are unreliable in consistently producing crystals that have both acceptable light output characteristics and material uniformity. This lack of consistency is undesirable because of its direct effect on detector resolution, photopeak shape and detector-to-detector consistency. As such, LuAP scintillation materials having unacceptable light output characteristics and/or material uniformity tend to be unusable for many applications due to decreased logging speeds and/or increasing tool-to-tool variations.